Vapor pressure, curves measurement

A-6 Altitude and Atmospheric Pressures, 578 A-7 Vapor Pressure Curves, 579 A-8 Pressure Conversion Chart, 580 A-9 Vacuum Conversion, 581 A-10 Decimal and Millimeter Equivalents of Fractions, 582 A-11 Particle Size Measurement, 582 . A-12 Viscosity Conversions, 583 A-13 Viscosity Conversion, 584 A-14 Commercial Wrought Steel Pipe Data, 585 A-15 ... 

Pure CIF3O2 is colorless as a gas or liquid and white as a solid. Some of its measured (68) physical properties are summarized in Table XX. Near its melting point the vapor pressure above liquid CIF3O2 was found to be reproducibly lower than expected from the vapor pressure curve given in Table XX. This indicates that close to the melting point some ordering effect occurs in the liquid. 

The accuracy of the pressure and temperature measurements was verified by measuring the vapor pressure curves and critical points for pentane and for toluene. Vapor pressures were measured by observing the formation of a liquid phase as pentane or toluene was injected into the constant-volume view cell under isothermal conditions. The observation of critical opalescence was used to determine the critical point. The measured vapor pressures and critical points are given in Table I. Vapor pressures deviate from... 

Solution The Henry s law constants are found by drawing the tangent lines to the vapor-pressure curves and measuring their slopes. Because these lines begin at the origins (x, = 0 and P, = 0), the slopes are just the intercept with the x, = 1 axis, or from Fig. 2, KAc =150 torr and /Cchi = 140 torr. The accuracy of this procedure is limited by how well the initial slopes can be determined from limited data. (See Problem 6.)... 

A good measure of the volatility is the vapor pressure. Figure 1 depicts the vapor pressure curves for Zr and Hf halides in the gas phase over the respective solids. As can be seen, the volatility decreases according to MC14 > MBr4> ML( > MF4 with M= Zr and Hf. Evidently, chlorides and bromides... 

The Integration of Clapeyron s Equation and the Vapor Pressure Curve.—The integration of Clapeyron s equation to got the vapor pressure curve over a liquid or solid from a measurement of the latent heat is one of its principal uses. We may write the integral of Eq. (4.3) in the form... 

Effect of UFe on the MoFe Solid-State Transformation. The temperature of the solid-state transformation of pure MoFe obtained by thermal analysis was —10.8 0.1°C. from cooling curves and —9.8 0.05°C. from heating curves. The value of —9.8°C. is considered the better one since supercooling occurred while determining cooling curves. Literature values for this solid-state transformation are — 8.7°C., obtained from the intersection of vapor pressure curves (3), —9.6°C., obtained in calorimetric measurements (2), and —9.68°C., also obtained in calorimetric measurements (14). 

The possibility of calculating thermodynamic functions from infrared and Raman frequencies has been exploited for Fe(05115)2, Ni(OsH5)2, and Ru(OsH6)2 (124)- The vapor-pressure curve of ferrocene was also reported soon after its discovery (112). Vapor-pressure measurements for dicyclopentadienyl manganese are also available (216). The heats of formation of Fe(05Hs)2 and Ni (05115)2 from the O5H6 radical and the... 

The region to the right of the vapor-pressure curve in Fig. 3.9 is called the superheated region and the one to the left of the vapor-pressure curve is called the sub-cooled region. The temperatures in the superheated region, if measured as the difference (0-N) between the actual temperature of the superheated vapor and the saturation temperature for the same pressure, are called degrees of superheat. For example, steam at 500 F and 100 psia (the saturation temperature for 100 psia is 327.8°F) has (500 — 327.8) = 172.2 F of superheat. Another new term you will find used frequently is the word quality. A wet vapor consists of saturated vapor and saturated liquid in equilibrium. The mass fraction of vapor is known as the quality. 

The curved line from T to C in Figure 13-17a is a vapor pressure curve obtained experimentally by measuring the vapor pressures of water at various temperatures (Table 13-8). Points along this curve represent the temperature-pressure combinations for which liquid and gas (vapor) coexist in equilibrium. At points above AC, the stable form of water is liquid below the curve, it is vapor. 

The determination of the vapor pressure of various compounds was reviewed by Wiedemann (49). He discussed the determination of vapor pressure by TG techniques based on the Knudsen effusion method. The sample holder that was employed is illustrated in Chapter 3 (Figure 3.6). For some measurements, a Pyrex glass cell having a diameter of about 15 mm was used. Four organic compounds were studied p-chlorophenyl-AT. Af-dimethyl urea (Monuron. a herbicide), p-phenacetin, anthracene, and benzoic acid, in the temperature range of 250-400 K. The vapor-pressure curves of these compounds, in the range from 0 10 Torr, are shown in Figure 4.49. The AHs values calculated were Monuron. 27.4 p-phenacetin 27.6 anthracene, 20.1 and benzoic acid. 20.7 kcalmole. 

The disadvantage of this type of saturation construction is that a large amount of liquid leaves the saturator unused. This liquid can be analyzed in a laboratory, reset to the initial concentration, and then reused as saturator-inserted material. If such a laboratory is not available the liquid must be disposed of. Such steady-state flowthrough saturators can only be implemented if vapor pressure curves are available for multicomponent mixtures, either as a table or function, or if these values can be measured by the user. 

The best device, however, is the quartz coil manometer, the coil of which can be heatedto500°C(in special cases to 600-700°C). In all cases the null point of the instrument must be checked after each measurement. Therefore the manometer should be provided with a heating coil, which doe snot need to be at the test temperature but must nevertheless be at a sufficiently high temperature to prevent condensation in the coil and in the capillary connections (which are likewise provided with a heating coil). With compensation to zero, the pressure is read off on the Hg manometer. In those cases where it cannot be ascertained by the usual method (with a thermometer and distillation flask) the boiling point is determined more accurately by extrapolation of the vapor pressure curve. 

We changed the ammonia concentration and water vapor pressure and measured the ammonia sensor s output under various combinations of the two. The sensor reading response took several seconds because responses took time even if water vapor pressure was varied while keeping ammonia concentration at zero. We attributed this response time to the responsiveness of the system as a whole. The sensor s output was tested in ambient temperature, which varies with time. The response time curve of sensor has been observed at different concentration. Our ammonia sensor is quite capable of detecting even low ammonia concentrations of about 0.01 ppm. 

The vapor pressure curve has been derived from current measurements, in essential agreement with earlier NBS data p ]. Three analytical ranges are used to obtain accuracy in the derivatives ... 

When all the dew points measured in this way are coimected, a steep curve to the right is the result, the so-called boiling pressure curve or vapor pressure curve (Fig. 11.7). It gives the values of pressure and temperature at which gas and... 

The vapor pressure curve of each component is rendered by two straight lines. The vapor pressure curve has a sharp bend at the triple point because of the difference between sublimation and vaporization enthalpy. The diagram offers the possibihty to extraploate measured vapor pressures. 

Heats of vaporization doubtless constitute the best experimental material for deducing such relationships. M. Dunkel has collected data for some years and has estimated from them the molar cohesion of the principal typical groups of organic molecules. The difficulty which arises here in contrast to the Fajans-v. Weinberg calculation of the primary valence forces is due to the fact that, because of the large absolute values in the first case, the effect of temperature on these forces, i.e. the influence of specific heats and of chemical constants, can be ignored, while the experimental vapor pressure curves would lead to completely erroneous heats of vaporization if the specific heats were neglected. Measurements at... 

In Fig. 7, the critical phase behavior of binary aqueous solutions of several selected hydrocarbons and additionally fluorobenzene is shown, most of them having been measured in our laboratory [3]. The dashed curve is the vapor pressure curve of pure water, and the solid lines are parts of the branches of the binary critical p T) curves that start from the critical endpoint llg (systems 9 and 10) or from the critical point of pure water CP(H20). Whereas naphthalene H- water (system 9) and biphenyl -f water (system 10) show class-II behavior, all other systems belong to class III according to the classification of van Konynenburg and Scott, and thus exhibit gas-gas equilibria of the second kind. The consequence is that naphthalene and biphenyl are completely miscible with water already at quite low pressures near the vapor pressure curve of pure water. This behavior is of interest for measurements in mixed solvents and for separations. 

Vapor pressure curves (Gaggeler 1994 Turler 1996 Gartner et al. 1997) give a measure of the volatility of compounds. In O Fig. 20.4, the vapor pressure curves of the monomeric gas over the respective solids for Zr and Hf tetrachlorides and -bromides and for Nb and Ta pentachlorides and -bromides are shown, respectively. Also shown are vapor pressure curves for Nb and Ta oxytrichlorides. These curves are calculated using tabulated standard... 

Additional Analytical Characterization. The many gasoline specifications require particular attention to be paid to the properties of reformate, as it is often the primary component of gasoline. Chief among these are the analyses that determine the volatility of the reformate. The vapor pressure is measured most commonly by the Reid vapor pressure method (6). The number is commonly referred to as RVP. Similarly, the distillation curve of reformate is monitored to determine the volatility. 

It is difficult to determine directly the liquid-vapor coexistence curves of metals by measurement of the coexisting densities of the two phases. Rather, the curves have been established indirectly from the intercepts of measured isochores (Figs. 3.17 and 4.10) with the vapor pressure curve Psat versus T. The coexistence curves determined in this way for cesium and rubidium are presented in Fig. 6.1. This figure shows a plot of the reduced densities of the coexisting liquid, p lPc, and vapor, PvIPc as a function of the reduced temperature TjT. The plot also shows the mean densities, = (l/2)(pi, + py), known as the diameters. ... 

Interpolation beriveen data For such common liquids as water, many refrigerants, and others, the vapor-pressure-temperature curve has been established at many points. For most liquids, however, only relatively few data are available, so that it is necessary frequently to interpolate between, or extrapolate beyond, the measurements. The curve on arithmetic coordinates (Fig. 7.1) is very inconvenient for this because of the curvature, and some method of linearizing the curve is needed. Most of the common methods stem from the Clausius-Clapeyron equation, which relates the slope of the vapor-pressure curve to the latent heat of vaporization... 

The most striking news that one learns when studying vapor-liquid phenomena is that not only does the vapor need to nucleate a liquid droplet to condense, but that also the liquid needs to nucleate a gas bubble to evaporate [24]. On the theoretical side, the simulation is made easier because the vapor is relatively simple to handle, on the experimental side, vapor pressure measurements in vapor-liquid equilibrium are fairly easy to perform. The Gibbs ensemble Monte Carlo method (Section 9.8) can be applied to the vapor-liquid equilibrium with considerable success vapor pressure curves, second virial coefficients, and other equilibrium properties can be calculated by molecular simulation, and, remarkably, good results can apparently be obtained by highly accurate ab initio quantum mechanical potentials [25a] or by simple empirical potentials [25b]. 

A comparison of the liquid temperatures and pressures with the equilibrium values indicated that, immediately after venting, the liquids were superheated the temperatures were higher than indicated by equilibrium conditions. As the pressure increased, the bulk-liquid temperature also increased, but at a rate considerably lower than indicated by equilibrium (saturated) conditions. Stratification of the liquid temperatures provided a surface condition which within a short time followed the equilibrium vapor-pressure curve, while the bulk of the liquid became subcooled. The liquid-surface locations were not well defined but the level measurements (capacitance) indicated that the surface was around the 20-in. height at the beginning. The vapor temperature increased from about 43 to 46.5 R during the pressure rise without any major fluctuations. 

The capacitance probes were installed in the single-phase flow test setup as shown by Fig. 1. The volumetric quality of the fluid was measured at the beginning and at the end of the test section. The capacitance probes were preceded by a pressure—temperature measuring section thus, the condition of the fluid with regard to the vapor pressure curve was known. 

This does not divorce these values from the measured vapor-pres sure curve of the individual species, because vapor pressure. (If the curves in Figure 5.4 were totally straight instead of being gently curved, then if we knew vapor-pressure curve for species i with complete accuracy. In Figure 5.4 none of the experimental data curves cross one another, and the curvature is more or less proportional to (a, so it makes sense that there could be a universal =f(Tr, (o) function. Chao and Seader proposed such a function for hydrocarbons the methods described in the next section also do this, but in a somewhat different way.)... 

In Example 7.1 we showed that for any pure species, we can calculate the fugacity from an EOS. In Chapters 7 and 9 we used only the little EOS, for which that calculation was easy. For more complex EOSs the mathematics become more complex, as shown in Appendix F, but in principle the procedure is the same. In Figure 10.8 at any value of P we could read the values of the BWR EOS specific volume corresponding to the vapor and the liquid. At the pressure corresponding to the vapor pressure, the calculated fugacities of these two should be equal. That is the method actually used to calculate the values of the saturation vapor pressure in most modem tables of thermodynamic properties. It has the merit that the PvT behavior of the liquid, and that of the vapor, and the vapor-pressure curve are all calculated from the same EOS, with the consequence that at the phase boundaries all the values are internally consistent. We might think that this divorces the calculated vapor pressures from the experimental vapor-pressure measurements, but it does not. The adjustable constants in the EOS are chosen to make the... 

The rotational lines of ammonia (NH3) below 250 cm can easily be identified in the Jovian spectrum, but they are less prominent on Saturn, and completely absent on Uranus and Neptune. A comparison of the vapor pressure curve of NH3 with the ambient temperatures on these planets indicates that the atmospheres of Uranus and Neptune are just too cold to contain much NH3 in gaseous form at the pressure levels pertinent to these measurements, that is, at pressures up to about one bar. If NH3 were pushed up with a pocket of gas from lower levels, it would first supercool and, eventually, form small ice crystals. Earth-based measurements of the microwave... 

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